Prader-Willi Syndrome

Molecular Genetics Clinical Laboratory- Prader-Willi Syndrome

INDICATIONS FOR TESTING:Prader-Willi syndrome is characterized by hypotonia and feeding difficulties in early infancy, followed by uncontrolled appetite and obesity in childhood. Most patients have some degree of cognitive impairment and often behavioral problems. Older patients have hypogonadism and infertility. This disorder is caused by the absence or inactivity of several paternally derived genes on chromosome 15, which can be caused by a small de novo deletion in region 15q11-q12 (~70% of cases), by uniparental maternal disomy of chromosome 15 (~25%), by chromosomal translocations (~1%) or by unknown etiology (~5%).

TESTING OFFERED:Testing is done using molecular cytogenetic FISH analysis with SNRPN, & D15S10 probes and a routine karyotype in the Cytogenetics Laboratory, as well as SNRPN gene methylation testing and molecular polymorphism analysis in the Molecular Genetic Laboratory. Specimens from parents are requested for UPD analysis.

TURN-AROUND TIME:Most testing is completed within a time of 21 days following specimen receipt. Prenatal testing is usually completed within 7 days from specimen receipt.

SPECIMEN REQUIREMENTS:All specimens should be kept at room temperature and shipped overnight in an insulated container.

Adults and Children:Two tubes of whole blood are required.

1) A tube of 4 cc whole blood collected in an EDTA (lavender top) tube is preferred. Whole blood collected with other anticoagulants is acceptable but not preferred.

2) A second tube with 3 cc of blood collected in sodium heparin (green top) tube is required. Lithium heparin and other anticoagulants are not acceptable.

Prenatal:Prenatal testing is usually not indicated since most cases of Prader-Willi syndrome are de novo and have a low risk for future pregnancies, except those with chromosomal rearrangements. Genetic counseling is advised.